Abra: A+ -> A
A year ago, LO Abra was destroying balance cores left and right. Sashbra was one of the most mindlessly splashable Pokemon for offensive builds because of its effectiveness against other frail teams, especially those built around a single sweeper. It was almost impossible to distinguish the two sets at first glance despite their vastly different strengths, which made it even more annoying to deal with. Abra was one of the most defining Pokemon of LC.
This is no longer the case for three reasons:
Abra hates trappers. Diglett easily revenge-kills LO Abra and brings Sashbra down to its sash, rendering it unable to check what it needs to. Beat Up variants take it further and eliminate Sashbra from play entirely, provided the Diglett user has enough Pokemon left. Gothita has been gaining popularity again, as it can usually get the KO it needs to, even if it is promptly revenge-killed by Diglett. Scarfed Gothita can switch into standard Psychic/HP Fighting/Dazzling Gleam/Energy Ball Abra's Psychic and 2HKO it about two thirds of the time; even if Gothita isn't successful, Abra will be hard-pressed to check anything with 1 HP. Calm Mind Gothita is even worse, as it renders standard Abra variants a liability by using them as set-up bait. Shadow Ball and Knock Off variants of Abra can beat Gothita on the switch but cannot prevent the revenge-kill. Trapinch is much rarer than Diglett or Gothita, but is able to trap non-Energy Ball Abra handily, with Berry Juice Trapinch being able to switch in safely as well. Eviolite Trapinch can revenge-kill all variants of Abra.
In addition, Sashbra simply isn't the catch-all check it used to be. Sweepers it had a good match-up against, such as Timburr and Bellsprout, aren't as popular as they used to be. Instead, Shellder has firmly established itself as one of the best sweepers in the metagame, if not the best; this has led to Berry Juice Magnemite, Sashbra's main competition as a safety net, seeing a resurgence. Heysup's SPL week 1 team has made Aipom more popular than ever at high levels of play. Croagunk runs Sucker Punch more frequently than before. Although much lower down on the threatlist, Nasty Plot Vullaby is also seeing more use.
Abra continues to be very potent on the right teams, but splashability is no longer its strongest trait. It can still effectively function as a safety net or wall-breaker, but needs to be paired with significant support against trappers and checks to specific wincons if it is to pull its weight throughout the match.
Vullaby: A -> A+
I feel that Fletchling has improved now that it no longer has competition as LC's premier sweeping bird, but when it comes to best overall LC Flying-type, Vullaby takes the cake. The physical offensive set in particular is extremely difficult to switch into, yet itself finds plenty of opportunities to get into play.
Vullaby thrives on the current metagame trends. Not only does it have fantastic synergy with Diglett and Trapinch, it immediately puts opponents using trappers on the back foot whenever it comes in on Diglett or Gothita, almost guaranteeing that something will be crippled. Dark spam is incredibly strong at the moment, and Vullaby is basically mandatory for those. In addition, the popularity of fish spam indirectly benefits Vullaby. Cottonee becoming the dominant Fairy-type over Spritzee and Snubbull means less teams have Pokemon that can switch into Vullaby safely. Archen has seen a decrease in usage. Snivy is just another Pokemon that Vullaby checks. Most importantly, Vullaby is one of the few viable hard checks to Foongus, and the only one that can put significant pressure on a variety of switch-ins instead of letting Foongus just activate Regenerator for free.
On top of the offensive set's sheer effectiveness, Vullaby is deceptively versatile. Offensive Vullaby's moveset may be fairly static, but its EV spread and even item can be adjusted to suit the team's needs, as well as grab a few surprise KOs. The ubiquity of offensive variants means that Defog is not always expected anymore (although Pawniard might switch in anyways if you don't have Diglett); it helps that with the prominence of Water-types to shut down Archen, Vullaby is now arguably the tier's best Defog user. Nasty Plot Vullaby's set of coverage moves actually matches quite well against popular threats, and it takes advantage of Vullaby's usual switch-ins as well.
Vullaby has Download Porygon's ridiculous 1v1ing capabilities, Pawniard's "how do I switch into this more than once" factor, and can even act as a solid pivot, though not quite on the level of Mienfoo. Its weaknesses to common Pokemon are minimal, and the drawbacks to using it are nonexistent. I would not be opposed to seeing Vullaby in S.
Cottonee: A- -> A
Normally I'm not a fan of Pokemon that lose momentum against so many important threats, but the variety of Pokemon that Cottonee is able to check and the amount of support it offers for its sweeper teammates often makes it tough to pass up. Carvanha, Corphish, and Shell Smashers are some of the top sweepers right now that Cottonee can mitigate for most of the battle. If they're on Cottonee's team instead, then Cottonee can Knock Off key defensive Pokemon that often switch into it, and provide Memento support to ease setup. Offensive Cottonee is probably its best set right now because it soft checks Pawniard instead of the other way around.
I think that even though they have completely different niches, it might be helpful to compare Cottonee to Chinchou in viability. Both of them check important groups of Pokemon, but are somewhat hindered by U-turn + Diglett combinations. Chinchou gains momentum for its own team with Volt Switch, whereas Cottonee tries to decrease the opponent's momentum with Encore, Stun Spore, and Memento. Cottonee helps sweeper teammates with Knock Off and Memento, whereas Chinchou can attempt to act as a win condition late game with a Scarf or Agility set. These comparisons aren't entirely accurate - for example, Chinchou's Volt Switch is arguably better for momentum than a somewhat predictable Encore, but Cottonee isn't as vulnerable to trappers - but it serves to show how both can be described about equally well as very splashable but not entirely consistent supportive Pokemon.
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Disagreeing with Porygon dropping because I don't see how it's gotten worse. Trace Porygon was never supposed to wall all six Pokemon on the opposing team, but it can still reliably and repeatedly check almost any one or two Pokemon, allowing plenty of flexibility for the rest of the team. Download Porygon may not be able to permanently cripple switch-ins the way Pawniard can, but is arguably just as, if not more difficult to switch into due to its higher damage with Download, greater coverage moves, and fewer checks. Neither set requires any support at all to perform its role, although Agility Porygon certainly appreciates it. Porygon does lose to Calm Mind Gothita, but Gothita carries its own set of disadvantages in being almost useless against teams that do not have one of the specific Pokemon that CM Gothita traps. To make up for it, certain metagame trends have favoured Porygon instead; for example, Trace Porygon's niche as one of two consistent Shellder counters that has reliable recovery, alongside Slowpoke, is more important than ever. Porygon is also able to countertrap Diglett and avoid being trapped by Magnet Pull Magnemite, two common teammates for Shellder.
I personally don't feel that Porygon is any worse than other S ranks, but if you do, it may also be worth considering whether Porygon is closer to the bottom of S or the top of A+.
Agreeing with Spritzee, as I don't think it makes sense for Spritzee to be ranked higher than Snubbull. Spritzee is to balance what Snubbull is to offense; where Spritzee has greater survivability and can support balance cores, Snubbull is harder to switch into and can support offensive teammates. On the other hand, Cottonee fits into both archetypes well because its unique typing and disruptive movepool allow it to check a greater variety of threats. Spritzee and Snubbull, while still very good, aren't as splashable, and are normally only worth using when you need an especially resilient Fighting-type check or a cleric.